Illegal instruction: 4

I get that "Illegal instruction: 4" while trying to run qsort. But mergesort works fine. LLVM is a pile of shit.

>>16
$ gdb
-bash: gdb: command not found
$ uname -a
Darwin MacBook-Pro-MacBook.local 17.3.0 Darwin Kernel Version 17.3.0: Thu Nov 9 18:09:22 PST 2017; root:xnu-4570.31.3~1/RELEASE_X86_64 x86_64